The present invention relates to a trailer slider system, and more particularly to an operating system and parking brake interlock for the locking pins thereof.
Heavy combination vehicles typically include a tractor and one or more trailers. Trailers often incorporate a movable subframe commonly referred to as a slider. A slider generally includes a pair of axles, a suspension, and an apparatus for adjusting and locking the position of the slider along the length of the trailer. Typically, a linkage is actuated and locking pins are moved to engage selected holes in the frame rails of the trailer. With the locking pins retracted from the holes, the slider position may be adjusted along the length of the frame rails. Once the slider reaches a desired position, the actuation element is operated and the locking pins are extended into the trailer frame holes.
One challenge with the use of a slider is ensuring that the locking pins are engaged in the holes before the tractor begins to pull the trailer. Disadvantageously, if the locking pins are not fully engaged, then it may be possible for the slider to move relative the trailer.
Various known systems interlock the parking brake to the locking pin position. In one of these systems, if the locking pins are not engaged, then a valve will be in a position preventing flow of pressurized air to the parking brake control valve. As is known, vehicle parking brakes typically include a large spring that moves to set the brake, preventing movement of the trailer. With the parking brakes set, the trailer cannot move. Thus, this known system prevents the trailer from moving unless the locking pins are engaged.
Trailers are equipped with an air supply line that is used to charge the trailer air reservoir and to retract the parking brakes. A parking brake control valve directs air to the parking brakes and then to the reservoir. This valve also prevents loss of reservoir pressure when the supply line is disconnected. The reservoir supplies pressurized air to operate the service brakes and is also used for various other applications on the trailer. Another known system provides a pin interlock valve that vents the supply line from the tractor and blocks any flow at the inlet to the parking brake control valve. Thus, in this known system when the interlock valve vents the supply of pressurized air, the reservoir will not charge.
Blocking the inlet to the parking brake control valve may actually lock the parking brakes in a release position if they are already released prior to the locking pins moving out of engagement. That is, if the parking brakes are released, and for whatever reason the pins are then withdrawn, the parking brakes cannot be set, and would stay in the released position. Furthermore, when the valve opens to vent the flow of air from the pressurized air supply line, the valve blocks the line leading to the parking brake control valve. This could potentially lock the air already in the parking brake chamber, again holding the brake away from the parked position.
Another problem with the prior art arrangement is that if the reservoir is not charged when the supply line is vented, there may not be air to drive accessories. Many of the locking pin drives are pneumatically powered and in the absence of pressurized air in the reservoir, these systems may not permit actuation of the locking pins.
Accordingly, it is desirable to provide a locking pin system that is readily actuated yet provides failsafe engagement of the slider with the trailer.